A conventional belt conveyance apparatus has an endless guide member in a part extending from an end surface of a conveyance roller on a conveyance belt so that the endless guide member is engaged with a partition plate provided on a side of ends of a drive roller and a driven roller (may be referred to as a follower roller or an idle roller) (for example, refer to patent document 1). According to the above structure, there is no stress generated in the endless guide member if the conveyance belt moves in a zigzag direction and a pressure force is exerted on the conveyance belt and an elongation occurs, and a flatness of the conveyance belt is maintained.
Additionally, there is a belt conveyance apparatus having a support frame for rotatably supporting a driven roller engaged with a conveyance belt and a support means for supporting a central portion of the support frame via a spring so as to support the driven roller in a seesaw state (for example, refer to patent document 2). According to this structure, if the conveyance belt tends to deflect on the driven roller, the driven roller shifts to follow the deflection, which results in correction of zigzag movement of the conveyance belt.
Moreover, there is a belt conveyance apparatus which countervails a deflecting force of a conveyance belt caused by a twist between axes of a drive roller and a driven roller by appropriately selecting a direction of twist of wefts (strings extending in a circumferential direction) and a number twist turns in a core material of the conveyance belt (for example, refer to patent document). Here, the conveyance belt in which a deflecting force opposite to the deflecting force of the drive mechanism of the conveyance belt is applied.
Further, there is a belt conveyance apparatus comprising a backup roller engaged with a conveyance belt provided with a bear, a transfer roller which sandwiches and presses the conveyance roller with the backup roller and disengageably engages with the backup roller, and a tension canceling means that cancels a tension when the conveyance belt is not driven, wherein when the tension of the conveyance belt is cancelled, the transfer roller is brought into contact with the conveyance belt so as to prevent the bead of the conveyance belt from being disengaged from the-backup roller (for example, refer to patent document 4).
Patent document 1: JP2003-095472,A (paragraphs 0011 and 0012 of page 3, FIG. 1, FIG. 2)
Patent document 2: JP04-246042,A (paragraph 0019 of page 3 to paragraph 0031 of page 4, FIG. 1)
Patent document 3: JP06-040591,A (paragraph 0016 of page 3 to paragraph 0020 of page 4, FIG. 1, FIG. 2)
Patent document 4: JP2000-284607,A (paragraphs 0085 to 0095 of page 8, FIG. 8, FIG. 9)
In the conventional belt driving apparatus, when a driven roller adjacent to a drive roller or a support shaft thereof is twisted relative to the drive roller or a support shaft thereof, if a conveyance belt is deflected relative to the axial direction of the driven roller, the support shaft of the driven roller tends to move in a direction opposite to a deflecting direction of the conveyance belt. However, with such a belt driving apparatus, since the support shaft of the driven roller engaged with a conveyance belt is restricted or fixed so as to not move in the axial direction (generally horizontal direction), it is considered that there is a case in which the driven roller cannot follow the deflection. Thus, it is desired to maintain further flatness of the conveyance belt and flatness of papers.